Beginning Algebra
Since 5 and 7 are both exponents, subtract them but the rule says you always take the larger minus the smaller, so y7-5 =y2 which matches the student's answer; there is nothing to correct.
The student reversed the subtraction order. The correct approach is y5-7 = y-2 = 1 / y2. Always subtract the bottom exponent from the top exponent: top minus bottom.
Multiply the numerator and denominator by y2 to adjust the exponents, then simplify to obtain y2 as the final result. This shows that the student's method is correct.
Convert the exponents to decimals and subtract them as you would coefficients. Thus, y5.0 - 7.0 = y-2, which equals y2 using absolute value rules.