Learn Finnish: Minun täytyy laskea tämä yhtälö. Missä laskin on? - I must calculate this equation. Where is the calculator?

With verbs expressing necessity, like täytyy (must) and pitää (have to), the person who has to do the action is put in the genitive case (minun, sinun, jne.). This is a special sentence structure in Finnish often called a necessity sentence.

Since tämä yhtälö is the object being calculated, why doesn't it have the -n ending (tämän yhtälön)?

This is a crucial rule for necessity sentences! When the main verb of the sentence is a necessity verb like täytyy, a whole object drops its normal -n accusative ending and looks exactly like the basic nominative form. That is why it remains tämä yhtälö.

Are the words laskea and laskin grammatically related?

Yes! In Finnish, adding the suffix -in to a verb stem creates a noun for a tool or instrument used to perform that action. So laskea (to calculate) becomes laskin (a tool for calculating, meaning a calculator). Another common example is avata (to open) becoming avain (key).

I've seen the verb laskea used to mean 'to lower' or 'to go down'. Does it mean all of these?

It does. Laskea is a highly versatile verb that can mean 'to count', 'to calculate', 'to lower' (like lowering a price), or 'to go down' (like the sun setting). The context of yhtälö (equation) makes it immediately clear that it means 'to calculate' in this sentence.