
Example: If a+b+c = 6 and a^{2}+b^{2}+c^{2} = 26, find the value of ab+bc+ca. Solution: Given that a+b+c = 6 Squaring on both sides, we get (a+b+c)^{2} = 6^{2} a^{2}+b^{2}+c^{2}+2(ab+bc+ca) = 36 26+2(ab++bc+ca) = 36 2(ab+bc+ca) = 3626 2(ab+bc+ca) = 10 ab+bc+ca = 10/2 ab+bc+ca = 5
Directions: Solve the following problems. Also write at least ten examples of your own. 