The formula for calculating the area of a right triangle is right angle side × right angle side ÷2(S= 1/2ab). A right triangle is a triangle with an angle of 90 degrees. The formula for calculating the area of a right-angled triangle is: right-angled side × right-angled side ÷2(S= 1/2ab). Right triangle is a kind of geometric figure. There are two kinds of right triangles: ordinary right triangle and isosceles right triangle.