Tanto si dibujas un triángulo como si dibujas un rectángulo, mide bien cada ángulo antes de seguir.

Yes. Tanto si ... como si ... is a very common way to express whether ... or ... in Spanish.

In this sentence:

• Tanto si dibujas un triángulo como si dibujas un rectángulo...

the pattern sets up two alternatives:

• if you draw a triangle
• or if you draw a rectangle

So grammatically, Spanish is using a fixed correlative structure:

• tanto si + clause + como si + clause

A shorter version si ... o si ... can sometimes be understood, but tanto si ... como si ... sounds more complete and idiomatic here.

Because the structure requires it on both sides:

• tanto si
• como si

Spanish treats both alternatives as parallel clauses, so each one keeps si.

That is different from English, where we usually say just whether X or Y without repeating if. In Spanish, repeating si is normal and expected in this pattern.

So:

• tanto si dibujas un triángulo como si dibujas un rectángulo

is the standard form, not a redundant one.

It is repeated to keep the sentence fully balanced:

• tanto si dibujas un triángulo como si dibujas un rectángulo

This is very natural Spanish.

Could you omit it? Sometimes in Spanish, repeated material can be dropped if it is obvious, but with this structure, repeating the verb usually sounds clearer and more natural. So learners should treat the full repetition as the safest option.

In other words, Spanish often likes this kind of symmetry more than English does.

Because here si means if, not whether in a subordinate clause that triggers the subjunctive.

With ordinary si clauses referring to real or general situations, Spanish normally uses the indicative:

• si dibujas
• si estudias
• si vienes

So in this sentence, dibujas is present indicative, second person singular.

The structure tanto si ... como si ... also normally takes the indicative when talking about general alternatives like this.

Because mide is the tú imperative of medir.

Compare:

• mides = you measure / you are measuring
• mide = measure!

The second part of the sentence is giving an instruction:

• mide bien cada ángulo antes de seguir

So it needs the imperative, not the present indicative.

For tú, the affirmative imperative of medir is mide.

The hidden subject is tú.

Spanish often leaves subject pronouns out when they are clear from the verb ending. Here:

• dibujas = you draw
• mide = measure! addressed to you

So the sentence is speaking directly to one person in the informal singular, which is very common in instructions, teaching, and textbooks.

If it were formal singular, you would expect:

• mida

If it were plural informal in Spain, you would expect:

• medid or more commonly a different instructional style, since vosotros imperatives can sound less common in educational wording depending on context.

Bien means something like carefully, properly, or accurately here.

It does not just mean well in a vague sense. In instructions like this, bien often strengthens the command and tells the person to do it thoroughly:

• mide bien = measure it properly / measure it carefully

This is a very natural use of bien in Spanish.

Cada means each. It focuses on the angles one by one.

So:

• mide bien cada ángulo

suggests checking every single angle individually.

If the sentence used los ángulos, the meaning would still be similar in practice, but cada gives a stronger sense of individual attention. That fits well with instructional language.

Also note that cada is followed by a singular noun:

• cada ángulo
• not cada ángulos

Because after antes de, Spanish uses an infinitive when the subject is the same as the subject of the main verb.

Here, the person who must measure is also the person who will continue. So Spanish uses:

• antes de seguir

This is very common:

• Lávate las manos antes de comer.
• Piensa antes de hablar.

If the subject changes, then Spanish normally uses antes de que + subjunctive:

• Hazlo antes de que llegue tu profesor.

So:

• same subject -> antes de + infinitive
• different subject -> antes de que + subjunctive

The comma separates the introductory conditional-alternative clause from the main instruction.

So the sentence has two parts:

1. Tanto si dibujas un triángulo como si dibujas un rectángulo
2. mide bien cada ángulo antes de seguir

That first long section sets the condition or framework, and the comma helps the reader process it before the main command arrives.

In English, we often do the same with an introductory clause.

Yes. They are part of the correct spelling and pronunciation.

All three words have the stress on the syllable with the written accent:

• tri-ÁN-gu-lo
• rec-TÁN-gu-lo
• ÁN-gu-lo

Without the accent marks, the words would be misspelled.

For learners, it is also useful to notice that these are all esdrújulas: words stressed on the third-to-last syllable. In Spanish, all esdrújulas always carry a written accent.

In this sentence, it is most natural to include un with each noun:

• un triángulo
• un rectángulo

That keeps both alternatives parallel and complete.

Spanish often repeats articles in coordinated structures more than English might. Since each option is a separate object of dibujas, repeating the article sounds normal and clear.

So learners should not worry that this is unnecessary repetition. It is standard Spanish.