A parallelogram has sides measuring 7 and 9. Its shorter diagonal has a length of 8. Find the measure of the longer diagonal.
Parallelogram Law : The sum of the squares of the four sides of a parallelogram = the sum of the squares of the diagonals
So
2*7^2 + 2*9^2 = 8^2 + x^2
98 + 162 = 64 + x^2
98 + 162 - 64 = x^2
196 = x^2
sqrt (196) = x = 14 = the longer diagonal
THAT is a really obscure law I did NOT know about !!
See here, EP :
https://en.wikipedia.org/wiki/Parallelogram_law
Good to know in my everyday life ..... haha Thanx ! ~ EP
LOL!!!!
