Question

como resolve isso:

* cos²(a+b) = ?
*cos²(a-b) = ?

Answer 1

$\displaystyle \cos^2(a+b)\\\cos^2(a-b)\\\\\\ \boxed{\cos^2(x)=\frac{1}{2}(1+\cos(2x))}\\\\\ i)~~\cos^2(a+b)= \frac{1}{2}(1+\cos(2a+2b))\\\\ ii)~\frac{1}{2}\cos(2a+2b)+1\\\\iii)\frac{1}{2}(\cos(2a)\cos(2b)-\sin(2a)\sin(2b))+1=\cos^2(a+b)\\\\\\\\\\\ i)~cos^2(2a-2b)=\frac{1}{2}(\cos(2a-2b))\\\\ii)\frac{1}{2}(\cos(2a)\cos(2b)+\sin(2a)\sin(2b))=\cos^2(a-b)$

cê pode encontrar as relações trigonométricas nessa tabela:
http://www.eqm.unisul.br/download/trig/