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प्रश्न
sin4A – cos4A = 1 – 2cos2A. For proof of this complete the activity given below.
Activity:
L.H.S = `square`
= (sin2A + cos2A) `(square)`
= `1 (square)` .....`[sin^2"A" + square = 1]`
= `square` – cos2A .....[sin2A = 1 – cos2A]
= `square`
= R.H.S
उत्तर
L.H.S = sin4A – cos4A
= (sin2A)2 – (cos2A)2
= (sin2A + cos2A) (sin2A – cos2A) .....[∵ a2 – b2 = (a + b)(a – b)]
= 1(sin2A – cos2A) .....[∵ sin2A + cos2A = 1]
= sin2A – cos2A
= 1 – cos2A – cos2A .....[sin2A = 1 – cos2A]
= 1 – 2cos2A
= R.H.S
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Activity: L.H.S. = cotθ + tanθ
= `cosθ/sinθ + square/cosθ`
= `(square + sin^2theta)/(sinθ xx cosθ)`
= `1/(sinθ xx cosθ)` ....... ∵ `square`
= `1/sinθ xx 1/cosθ`
= `square xx secθ`
∴ L.H.S. = R.H.S.
