Which of the following expression(s) are fourth-degree trinomials? Select all that apply.

A.
3x^2y + 5x^3y + 6y^4
B.
6y^4 + 5x^3 + 1
C.
5xy − 5x^2y^2 + 7
D.
3y^3 + 3x^3y^3

this doesn't make sense lol

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