One side of the rectangle is 3cm. Kolya increased the other side of this rectangle by 5cm.

One side of the rectangle is 3cm. Kolya increased the other side of this rectangle by 5cm. How many square centimeters have you increased the area?

Let the other side of rectangle A.

S1 area of rectangle: S1 = 3 * A.

If Kolya increases the side of the rectangle by 5 cm, then the length of the side becomes A + 5.

Then the area S2 of the rectangle becomes:

S2 = 3 * (A + 5).

notice, that

S2 = 3 * (A + 5) = 3 * A + 15 = S1 + 15,

S2 – S1 = 15 cm ^ 2.

Answer: Kolya increased the area of the rectangle by 15 square cm.