waecmaths question:
The interior angle of a pentagon are (2x + 5)o, (x + 20)o, xo, (3x – 20)o and (x + 15)o. Find the value of x
Option A:
80o
Option B:
70o
Option C:
65o
Option D:
40o
waecmaths solution:
The sum of angles in a pentagon is 540o$\begin{align} & {{(2x+5)}^{\circ }}+{{(x+20)}^{\circ }}+{{x}^{\circ }}+{{(3x-20)}^{\circ }}+{{(x+15)}^{\circ }}={{540}^{\circ }} \\ & {{(8x+20)}^{\circ }}={{520}^{\circ }} \\ & x={{65}^{\circ }} \end{align}$
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