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Areas Of Parallelograms And Triangles

Question
CBSEENMA9002604

In the given figure, AE bisects ∠DAC and ∠B = ∠C, prove that AE || BC.


Solution

Given: AE bisects ∠DAC and ∠B = ∠C
To Prove: AE || BC
Proof: In ∆ABC,
Ext. ∠DAC = ∠ABC + ∠ACB    ...(1)
| An exterior angle of a triangle is equal to the sum of its two interior opposite angles
⇒ ∠DAC = ∠ACB + ∠ACB
| ∵ ∠B = ∠C (Given)
⇒ ∠DAC = 2∠ACB
⇒ 2∠CAE = 2∠ACB
left enclose table row cell because space AE space bisects space angle DAC end cell row cell therefore space angle CAE equals angle DAE equals 1 half angle DAC end cell end table end enclose
⇒ ∠CAE = ∠ACB
But these angles form a pair of equal alternate interior angles
∴ AE || BC