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How do you prove #2cos^2 x - sinx - 1 = 0#?

1 Answer

Apr 15, 2015

You can't prove it. It's not true.

Let #x= pi/4# then we get:

#2 cos^2x - sinx -1 = 2 cos^2 (pi/4) - sin (pi/4) -1#

#color(white)"sssssssssssssssssss"# #= 2 (1/sqrt2)^2- sqrt2/2-1#

#color(white)"sssssssssssssssssss"# #= 1- sqrt2/2-1#

#color(white)"sssssssssssssssssss"# #= - sqrt2/2#

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