if 7 parallel lines in a plane is intersected by a family of another 8 parallel lines , how many parallelograms are there in the network thus formed ?
"parallelogram can formed by 2 horizontal and 2 vertical lines for horizontal 7 c 2 for vertical 8 c 2 total parallelogram is 7 c 2 * 8 c 2 = 21 * 28 = 588 answer : a"
multiply(divide(multiply(7, subtract(7, const_1)), const_2), divide(multiply(8, subtract(8, const_1)), const_2))