Classifying a triangle

Which classification best describes the triangle?
The measures of the angles of a triangle can be represented
by the expressions x°, (x + 20)°, and (2x)°. 

Angles of a triangle add up to 180°

x + x + 20 + 2x = 180 {added angles up and set equal to 180}
4x + 20 = 180 {combined like terms}
4x = 160 {subtracted 20 from both sides}
x = 40 {divided both sides by 4}
x + 20 = 60 {substituted 40, in for x, into x + 20}
2x = 80 {substituted 40, in for x, into 2x}

40°, 60°, and 80° are the angles
The triangle is an acute triangle {none of the angles are greater than/equal to 90°}

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