Two sides of a triangle measure 10cm and 18cm . which could be the measure of the third side of the triangle? a. 6cm b. 8cm c.12cm d.30cm

It cannot be 30, because the sum of two sides should be more than third side
-not D
10+18=28 <30

it cannot be 6 +10 < 18

it cannot 8
8+10=18

so it is has to be C) 12
12+18>10
10+12>18
10+18>12
answer  C. 12 cm

First subtract 10 from both side
y^2+6y-16=0
(y+8)(y-2)=0
-8 and 2