Question

Tolong di jawab ya ..
Segitiga ABC siku siku di C dengan cos A cos B =
. Nilai dari cos ( A - B ) =.....
A. 0
B.
C.
D.
E. 1

Answer 1

A+B+C = 180
A+B+90 = 180
A+B = 90
cos (A+B) = c0s 90
cos A.cos B - sin A.sin B = 0
2/5 - sinA.sinB = 0
sinA.sinB = 2/5

maka
cos(A-B) = cosA.cosB + sinA.sinB
             = 2/5 + 2/5
             = 4/5

Semoga membantu ya :)

Answer 2

2 cos A cos B = 2 x 2/5
cos (A + B) + cos (A - B) = 4/5
cos (180 - C) + cos (A - B) = 4/5
- cos C + cos (A - B) = 4/5
- cos 90° + cos (A - B) = 4/5
0 + cos (A - B) = 4/5
cos (A - B) = 4/5