Write the equation in standard form of the circle where center (-2,0) and radius 5​

x²+y²+4x-21=0

Step-by-step explanation:

(x-h)²+(y-k)²=r²

(x--2)²+(y-0)²=(5)²

(x+2)²+y²=25

x²+4x+4+y²=25

x²+y²+4x-21=0

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