prove that cos 70+ sin40 = cos10
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Answered by
19
We know that
sin40= sin ( 90-50) = cos 50
&
cosA + cosB = 2 cos ( A+B/2) cos ( A-B/2)
L.H.S
= cos70+ Cos 50
= 2 cos ( 70+50/2) cos ( 70-50/2)
= 2 cos 60 cos 10
= 2 *1/2 cos10
= cos10°
hope helped!
sin40= sin ( 90-50) = cos 50
&
cosA + cosB = 2 cos ( A+B/2) cos ( A-B/2)
L.H.S
= cos70+ Cos 50
= 2 cos ( 70+50/2) cos ( 70-50/2)
= 2 cos 60 cos 10
= 2 *1/2 cos10
= cos10°
hope helped!
Sampath365:
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