Question

Find The Value Of :( cos20° /sin70°) + (cos70°/sin20°) - 8sin²30°
(class 10 CBSE SAMPLE PAPER 2017-18 MATHS)

Answer 1

Evaluate:


( cos20° /sin70°) + (cos70°/sin20°) - 8sin²30°



SOLUTION:



( cos20° /sin70°) + (cos70°/sin20°) - 8sin²30°


= ( cos(90°- 70°) /sin 70°) + (cos(90°- 20°)/sin 20°) - 8sin²30°


[ cos(90 -A)=  sinA]


=( Sin 70° /sin 70° )+ (sin20° /sin20 ° ) - 8(½)²


[ sin 30° = ½]


= 1+ 1- (8×1/4)


= 1+1 -2


= 2-2


= 0


Hope this will help you...