It is given that △ABC≅△FDE and AB=5 cm,∠ B=40∘ and ∠A=80∘. Then which of the following is true? (A) DF=5 cm,∠F=60∘ (B) DF=5 cm,∠E=60∘ (C) DE=5 cm,∠E=60∘ (D) DE=5 cm,∠D=40∘
Solution
In △ABC,∠A=80∘,∠B=40∘ and ∠C=x (assume)
∵∠A+∠B+∠x=180∘ (angle sum property of a triangle)
⇒80∘+40∘+x=180∘⇒x=180∘−120∘⇒x=60∘⇒DC=60∘∵△ABC≅△FDE
By ASA congruence relation
AB=FD,∠ A=∠F,∠ B=∠D
⇒DF=5 cm,∠F=80∘,∠B=40∘=∠D∵ Also, ∠C=∠E⇒∠E=60∘
Therefore, DF=5 cm,∠E=60∘
Hence option (B) is correct.
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