Need answer to question 19 please !!

(1/3) / (x+1) + (-1/3) / (x+4)

Step-by-step explanation:

1 / (x+1)(x+4) = (A/x+1) + (B/x+4)

1 =  ((A/x+1) + (B/x+4)) * (x+1)(x+4)

1 = A*(x+4) + B*(x+1)

* if x = -4

1 = A*(-4+4) + B*(-4+1)

1 = B*(-3)

B = -1/3

** if x = -1

1 = A*(-1+4) + B*(-1+1)

1 = A*(3)

A = 1/3

check: (1/3)/(x+1) + (-1/3)/(x+4) = ((1/3)*(x+4))/((x+1)(x+4)) + ((-1/3)*(x+1))/((x+1)(x+4))

==> ((1/3x + 4/3)+(-1/3x - 1/3)) / ((x+1)(x+4)) = 1 / (x+1)(x+4)

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4