Question

cos 10 cos 50 cos 70=root 3/8

Answer 1

= (cos 10 cos 50) cos70
=1/2(2cos10cos50)cos70
=1/2{(cos(50+10) +cos(50-10)} cos70
=1/2(cos60+ cos40) cos70. we know cos 60 value is 1/2. so this value will put in the next step
=1/2(1/2+cos40)cos70
=1/2(cos70/2 +cos70cos40)
=1/2(cos70 +cos70 cos40/2) take LCM
=1/4(cos70+ 2 cos70cos40)
=1/4(cos70+ cos110+ cos30)
=1/4(cos70+cos(180-70)+ cos30)
=1/4(cos70-cos70 +cos30) { -cos 70 is in 2nd quadrant.}
=1/4×√3/2
=√3/8
proved.

Answer 2

Answer:

There is your solution..

Hope it's help you.