Prove, using a combinatorial (counting) argument, that c(2n, 2) = 2c(n, 2) + n 2

Two sides of a triangle mesure 20cm and 30cm. what is the measure of the third side

At the beginning of the day, stock xyz opened at $6.12. at the end of the day, it closed at $6.88. what is the rate of change of stock xyz? a. 1.17% b. 11.0% c. 12.4% d. 81.5%

Find the area of the triangle shown 3 by 6