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Question
If sin θ + cos θ = `sqrt(3)`, then show that tan θ + cot θ = 1
Solution
sin θ + cos θ = `sqrt(3)` ......[Given]
∴ (sin θ + cos θ)2 = 3 ......[Squaring on both sides]
∴ sin2θ + 2sinθ cosθ + cos2θ = 3 ......[∵ (a + b)2 = a2 + 2ab + b2]
∴ (sin2θ + cos2θ) + 2sinθ cosθ = 3
∴ 1 + 2 sin θ cos θ = 3 ......[∵ sin2θ + cos2θ = 1]
∴ 2 sin θ cos θ = 2
∴ sin θ cos θ = 1 ......(i)
tan θ + cot θ = `sintheta/costheta + costheta/sintheta`
= `(sin^2theta + cos^2theta)/(costhetasintheta)`
= `1/(sintheta costheta)` ......[∵ sin2θ + cos2θ = 1]
= `1/1` ......[From (i)]
= 1
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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`
