The base of the triangle is 42 cm, and the height is 10% shorter than the base, the area of the triangle is calculated.

1) 100% – 10% = 90 (%) from the base leaves the height of the triangle.

2) 90%: 100% = 0.9 (part) from the base leaves the height of the triangle.

To find the value of the fractional part of the whole, you need to multiply the value of the whole part by the fraction, which means the fractional part.

Those. the length of the base must be multiplied by 0.9:

3) 42 * 0.9 = 37.8 (cm) the height of the triangle.

The area of a triangle is calculated by the formula:

S = 1/2 * a * h, where S is the area, a is the base, h is the height lowered to the base.

4) 1/2 * 42 * 37.8 = 793.8 (sq. Cm)