NCERT Solution Class IX Mathematics Triangles Question 1 (Ex 7.4)

Question 1:

Show that in a right angled triangle, the hypotenuse is the longest side.

Answer:

 

Let us consider a right-angled triangle ABC, right-angled at B.

In ∆ABC,

∠A + ∠B + ∠C = 180° (Angle sum property of a triangle)

∠A + 90º + ∠C = 180°

∠A + ∠C = 90°

Hence, the other two angles have to be acute (i.e., less than 90º).

∠B is the largest angle in &ABC.

∠B > ∠A and ∠B > ∠C

AC > BC and AC > AB

[In any triangle, the side opposite to the larger (greater) angle is longer.]

Therefore, AC is the largest side in ∆ABC.

However, AC is the hypotenuse of ∆ABC. Therefore, hypotenuse is the longest side in

a right-angled triangle.

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