[re]:question 32 c

when the calculator simplifies (1/r-1/x)/(r-x), it puts the (1/r-1/x) over a common denominator then multiplies the result by 1/(r-x). It factors out negative 1 from (r-x) to -1(x-r), in the denominator and that cancels the x-r in the numerator, (from finding common denominator first. Finally, you are left with 1/rx times -1, which equals -1/rx.