In an isosceles triangle, if the vertex angle is twice the sum of the base angles, then the measure of vertex angle of the triangle is `100^0` (b) `120^0` (c) `110^0` (d) `130^0`

Explanation

Solution: Let each base angle be x in an isosceles `triangleABC`
Then vertex angle be `2(x+x)=4x`
Since sum of angles of a triangle is `180^@`
Hence, `4x+x+x= 180^@`
`6x`= `180^@`
`x`=`30^@`

`therefore` vertex angle = `4 times 30^@`=`120^@`
So,option (b) is correct.