In `Delta ABC,`if BC=AB and `angleB=80^(@)`,then `angleA` is equal to

Options

A. `80^(@)`
B. `40^(@)`
C. `50^(@)`
D. `100^(@)`

Answer

C

Explanation

Given,`DeltaABC` such that BC=AB and `angleB=80^(@)`
in `DeltaABC, " " AB =BC `
`rArr " " angleC=angleA`
[angles opposite to equal sides are equal ]
We know that, the sum of the angles of a tringle is `180^(@)`
` therefore " " angleA+angleB+angleC=180^(@)`
`rArr " " angleA + 80^(@) +angle A=180^(@)`
`rArr " " 2 angleA=180^(@)-80^(@)=100^(@)`
`rArr" " angleA(100^(@))/(2)`
`rArr " "angleA=50^(@)`