The base of a right-angled triangle is 10 and hypotenuse is 20. What is its area?

86.6 

Applying pythagoras theoram:

(20)² = (10)² + (Perpendicular)² 

400 = 100 + (Perpendicular)²

300 = (Perpendicular)²

Perpendicular = \(\sqrt { 300}\) = 10\(\sqrt { 3}\) 

\(\sqrt { 3}\) = 1.732

Perpendicular = 10 x 1.732 = 17.32 

Area = \(\frac{1 }{ 2}\) x b x h

Area = \(\frac{1 }{ 2}\) x 10 x 17.32

Area = 86.6