1.

ΔDEF is right angled at E. If m∠F = 30°, then find the value of (cos D – 1/√2). 1). -1/22). (√6 – 1)/√33). (√2 – 2)/2√24). √3 – 2

Answer»

We KNOW, SUM of all the ANGLES of a triangle is 180.

⇒ ∠D + ∠E + ∠F = 180°

 ⇒ ∠D + 90 + 30 = 180°

⇒ ∠D = 60°

∴ (cosD – 1/√2) = cos 60° – 1/√2 = 1/2 – 1/√2 = (√2 – 2­­)/2√2


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