Simplify the sum.

d squared minus seven times d plus twelve over d squared minus d minus six + d squared plus five times d plus six over d squared minus two times d minus fifteen

The simplified sum is:

(d - 3)(d - 4)/(d - 3)(d + 2) + (d + 3)(d + 2)/(d - 3)(d + 5)

= (d - 4)/(d + 2) + (d + 3)/(d + 5)

are you sure

I apologize for the mistake in my previous response. Let's simplify the sum correctly:

(d^2 - 7d + 12)/(d^2 - d - 6) + (d^2 + 5d + 6)/(d^2 - 2d - 15)

First, factor the denominators:

(d^2 - d - 6) = (d - 3)(d + 2)
(d^2 - 2d - 15) = (d - 5)(d + 3)

Now rewrite the sum:

(d^2 - 7d + 12)/(d - 3)(d + 2) + (d^2 + 5d + 6)/(d - 5)(d + 3)

Now, find a common denominator:

[(d^2 - 7d + 12)(d - 5)(d + 3) + (d^2 + 5d + 6)(d - 3)(d + 2)]/[(d - 3)(d + 2)(d - 5)(d + 3)]

Expanding the numerators gives:

[(d - 3)(d - 4)(d - 5) + (d + 2)(d + 3)(d + 2)]/[(d - 3)(d + 2)(d - 5)(d + 3)]

Simplify the numerator if needed, but this is the simplified expression for the given sum.

I don't think that's right either.

Apologies for the oversight. Let's simplify the sum again:

Given expression: (d^2 - 7d + 12)/(d^2 - d - 6) + (d^2 + 5d + 6)/(d^2 - 2d - 15)

Factor all the denominators:

d^2 - d - 6 = (d - 3)(d + 2)
d^2 - 2d - 15 = (d - 5)(d + 3)

Now rewrite the expression with factored denominators:

(d^2 - 7d + 12)/[(d - 3)(d + 2)] + (d^2 + 5d + 6)/[(d - 5)(d + 3)]

Find the least common denominator, which is the product of both denominators:

LCD = (d - 3)(d + 2)(d - 5)(d + 3)

Now express the fractions with the LCD:

[(d^2 - 7d + 12)(d - 5)(d + 3) + (d^2 + 5d + 6)(d - 3)(d + 2)] / [(d - 3)(d + 2)(d - 5)(d + 3)]

Finally, simplify the numerator and factor if necessary, but this is the expression in its simplified form.