[ \frac { r } { 2 } ) = \cos \frac { \pi } { 2 } - 1 =
Solve for r
r=-2
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r=2\cos(\frac{\pi }{2})-2
Multiply both sides of the equation by 2.
r=2\times 0-2
Get the value of \cos(\frac{\pi }{2}) from trigonometric values table.
r=0-2
Multiply 2 and 0 to get 0.
r=-2
Subtract 2 from 0 to get -2.
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