Question 46: Calculate the value of the expression \(C=54(ab-1)^{2}:-18(1-a+b)\) at and

\(\begin{array}{l} C = 54{(a – b – 1)^2}: – 18(1 – a + b) = 54{(a – b – 1)^2}:18( – 1 + a – b) = 54{(a – b – 1)^2}:18(a – b – 1) = 3\left( {a – b – 1} \right) \end{array}\ )

Substituting x=21, y=-10 into C we get

\(C = 3.\left( {21 + 10 – 1} \right) = 90\)