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प्रश्न
Prove that `(sintheta + "cosec" theta)/sin theta` = 2 + cot2θ
उत्तर
L.H.S = `(sintheta + "cosec" theta)/sin theta`
= `sintheta/sintheta + ("cosec"theta)/sintheta`
= 1 + cosec θ × cosec θ ......`[∵ "cosec" theta = 1/sin theta]`
= 1 + cosec2θ
= 1 + 1 + cot2θ .......[∵ 1 + cot2θ = cosec2θ]
= 2 + cot2θ
= R.H.S
∴ `(sintheta + "cosec" theta)/sin theta` = 2 + cot2θ
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Activity:
L.H.S = `square`
= `square/sintheta + sintheta/costheta`
= `(cos^2theta + sin^2theta)/square`
= `1/(sintheta*costheta)` ......`[cos^2theta + sin^2theta = square]`
= `1/sintheta xx 1/square`
= `square`
= R.H.S
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Solution:
In Δ ABC, ∠ABC = 90°, ∠C = θ°
AB2 + BC2 = `square` .....(Pythagoras theorem)
Divide both sides by AC2
`"AB"^2/"AC"^2 + "BC"^2/"AC"^2 = "AC"^2/"AC"^2`
∴ `("AB"^2/"AC"^2) + ("BC"^2/"AC"^2) = 1`
But `"AB"/"AC" = square and "BC"/"AC" = square`
∴ `sin^2 theta + cos^2 theta = square`
