# trig

I am almost finished iwth my questionings:)

Solve the given triginometric equation analytically

sin4x - cos2x = 0

Priya

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1. let's use the identity
sin2A = 2sinAcosA on the first term only

2sin2xcos2x - cos2x = 0 , now a common factor

cos2x(2sin2x - 1) = 0
cos2x = 0 or sin2x = 1/2

so 2x = 90, 270, 30, 150º
then x = 45,135,15,75º

but the period of sin2x and cos2x is 180º

to change these quickly to radians, take the smallest degree angle which is 15º
all other angles are multiples of 15
eg. 315 = 21*15
so 315º = 21pi/12 etc.

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2. Given angle 1 = (x + 7)degree, angle 2 = *(2x -3)degree, angle ABC = (x 2nd power) degree, angle D = (5x - 4)degree. Show that angle ABC congruent to angle D

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