Hey.

"Longest side of an isosceles right triangle." is your key.



First property to use: Right triangle means that if three sides are of length a, b and c with c the length of the side opposite to the right angle, we know 2 things. c is the longest side and
c^2 = a^2 + b^2.

Second property: If you have a right triangle, you can find the area of the triangle if you know the length of the two sides that hold the right angle. area of our triangle is (1/2)*a*b

Now in the case of an isosceles right triangle, 2 sides are equal. So in this case we have a and b are equal. b and c cannot be equal. a and c also cannot be equal. This is because c is the length of the hypotenuse and has to be the longest side. Right?
And area is (1/2)*a*a

So in this question we have a=b
Applying this in
c^2 = a^2 + b^2 = c^2 = a^2 + a^2
This can help us find the value of a as c is given.

Now area is (1/2) a^2.

Did I help you? Let me know by thanking me
If I did not, I am sorry. PM me, I will give you a more detailed explanation.