a positive number when decreased by 4 is equal to 21 times the reciprocal of the number . the number is :
let the number be x x - 4 = 21 / x x ^ 2 - 4 x - 21 = 0 ( x - 7 ) ( x + 3 ) = 0 x = 7 correct answer d
divide(add(sqrt(add(multiply(4, 21), power(4, const_2))), 4), const_2)