Question

-2 cos 75* cos 15* adalah.......

Answer 1

Answer:

$\large\boxed{-\frac{1}{2}=-0.5 }$

Step-by-step explanation:

To solve this problem, first you have to identify of cos from left to right numbers.

Given:

-2 cos 75* cos 15*

Solutions:

Use identify of cos formula.

$\large\boxed{\textnormal{Cos Formula}}$

$\displaystyle cos(s) cos(t)= \frac{cos(s+t)+cos(s-t)}{2}$

$\displaystyle\frac{cos (75+15)+cos(75-15)}{2}$

$\displaystyle -2*\frac{cos(75+15)+cos(75-15)}{2}$

Solve.

$\displaystyle -2*\frac{cos(75+15)+cos(75-15)}{2}=-cos(90)-cos(60)$

$\displaystyle cos(90)=0$

$\displaystyle cos(60)=\frac{1}{2}$

$\displaystyle -0-\frac{1}{2}=-\boxed{\frac{1}{2}}$

$\large\boxed{-\frac{1}{2}=-0.5 }$

The correct answer is -1/2=-0.5.