Answer as a fraction: AB = 127/13 (exact)
Answer in decimal form: AB = 9.76923 (approximate)
Sides AC and BC are the same length as AB.
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Work Shown:
AB = (3/2)x+4
AC = (1/5)x+9
These sides are equal to each other since all sides of an equilateral triangle are the same length.
AB = AC
(3/2)x+4 = (1/5)x+9
10*[ (3/2)x+4 ] = 10*[ (1/5)x+9 ] ... see note below
10*(3/2)x + 10*4 = 10*(1/5)x + 10*9
15x + 40 = 2x + 90
15x-2x = 90-40
13x = 50
x = 50/13
Note: I multiplied both sides by the LCD (lowest common denominator) 10 to clear out the fractions.
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Once we know what x is, we plug it into the expression for AB
AB = (3/2)x+4
AB = (3/2)*(50/13) + 4
AB = (3*50)/(2*13) + 4
AB = (3*2*25)/(2*13) + 4
AB = (3*25)/(13) + 4
AB = 75/13 + 4
AB = 75/13 + 52/13
AB = (75+52)/13
AB = 127/13 which is exact
AB = 9.76923 which is approximate
Because we have an equilateral triangle, AB = BC = AC.
