In triangle △abc, ∠abc=90°,
bh is an altitude. find the missing lengths.

ab=9, and ac=12 find hc.

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Work Shown:

Let x = HC and y = BH

AH = 12-x since AH = 12-HC and x = HC

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See the attached drawing below. The altitude BH forms three similar triangles which makes the proportion below possible

HC/BH = BH/AH

x/y = y/(12-x) ... substitution

x(12-x) = y^2 ... cross multiply

y^2 = -x^2+12x

note how I isolated y^2 instead of y. We will use this equation later.

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Focus on triangle AHB. Use the pythagorean theorem

(BH)^2 + (AH)^2 = (AB)^2

(y)^2 + (12-x)^2 = (9)^2

y^2 + 144-24x+x^2 = 81

-x^2+12x + 144-24x+x^2 = 81 ... replace y^2 with -x^2+12x

-x^2+12x + 144-24x+x^2-81 = 0

-12x + 63 = 0

-12x = -63

x = -63/(-12)

x = 5.25 <<-- answer in decimal form

x = 5 + 0.25

x = 5 + 1/4

x = 20/4 + 1/4

x = 21/4 <<-- answer as a fraction

i think it is everything has to equal 180 so, if i correct 4=c. 6=d. 8=a. 7=b. and the last question would be c. because they are parallel lines and they are congruent.

step-by-step explanation:

the reason everything has to equal to 180 is because that is how it works. i'm guessing that is its rule. 4 and 8 are congruent and parallel so, that would be 30+30 because they have the same number. it would equal 60. 6 and 7 are congruent and parallel so, that would be 30+30 because they have the same number. it would equal 60. 60+60 is 180. so, now you have your answer