Concept:Use index laws to combine powers with the same base.A negative exponent is rewritten as a reciprocal to make it positive.Explanation:The expression is a−5a−3⋅a−4.In the numerator, apply the product law: a−3⋅a−4=a−3+(−4)=a−7.Now apply the quotient law: a−5a−7=a−7−(−5)=a−2.To write it with a positive exponent, use a−m=am1.So, a−2=a21.Thus the positive exponential form is a21.Answer:a21