Trigonometry

[Stefany]

Does anybody know a formula that can verify that the left side is equal to the right side?
I tried proving the left side... But I don’t know if it’s correct.

 

[lev888]

I would try applying cos of sum formulas to the left side.

 

[Stefany]

But they’re opposite of each other, so won’t they just cancel each other out?

 

[lev888]

But they’re opposite of each other, so won’t they just cancel each other out?

Please post your work.

 

[Stefany]

 

[lev888]

Add missing parentheses and multiply. Then use sin²+cos²=1

 

[Stefany]

Is this what I was supposed to get after multiplying?

 

[lev888]

You found the right formulas for cos of a sum/difference. But you didn't apply them correctly - you didn't put each expression inside a set of parentheses. You have a product. You replace each factor by a sum. Each sum MUST be in parentheses. Please correct this. Then multiply the 2 sums. Then use sin²+cos²=1 to further simplify the result.

 

[Stefany]

Like this?

 

[lev888]

Like this?View attachment 18342

Looks good.