if 9 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 9 c 2 for vertical 8 c 2 total parallelogram is 9 c 2 * 8 c 2 = 36 * 28 = 1008 answer : d"
multiply(divide(multiply(9, subtract(9, const_1)), const_2), divide(multiply(8, subtract(8, const_1)), const_2))