`DeltaABC` में, AB=BC,`angleBAC=40^(@)` हे, तब `angleB` का बाह्य कोण ज्ञात करे?

Options

A. `90^(@)`
B. `70^(@)`
C. `110^(@)`
D. `80^(@)`

Explanation

According to question,
Given,

`angleA=40^(@)` AB=AC
`therefore angleB=angleC`
In `DeltaABC`
`angleA+angleB+angleC=180^(@)`
`40^(@)+2angleB=180^(@)`
`2angleB = 180^(@)-40^(@)`
`2angleB=140^(@)`
`angleB=70^(@)`
`therefore` External angle at B = `180^(@)-70^(@) = 110^(@)`