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प्रश्न
Verify cos3A = 4cos3A – 3cosA, when A = 30°
उत्तर
L.H.S = cos3A
= cos3(30°)
= cos90°
= 0
R.H.S = 4cos3A – 3cosA
= 4cos330° – 3cos30°
=`4(sqrt(3)/2)^3 - 3(sqrt(3)/2)`
= `(4 xx 3sqrt(3))/8 - (3sqrt(3))/2`
= `(3sqrt(3))/2 - (3sqrt(3))/2`
= 0
∴ L.H.S = R.H.S
Hence it is proved.
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