I know this is like the 700th question I've asked

BC = 15

Step-by-step explanation:

Because of parallel lines, AD and BE, triangles ADC and BEC are similar.

In similar triangles, the lengths of corresponding sides are proportional.

AC/BC = DC/EC

We see that AC = AB + BC = 3 + BC

Also, DC = DE + EC = 2 + 10 = 12

(3 + BC)/BC = 12/10

(3 + BC)/BC = 6/5

Cross multiply.

5(3 + BC) = 6BC

15 + 5BC = 6BC

15 = BC

BC = 15

14

step-by-step explanation:

x = ±sqrt(10)

step-by-step explanation:

5 - 2x² = -15

subtract 5 from each side

5-5 - 2x² = -15-5

-2x^2   = -20

divide by -2 on each side

-2x^2   /-2= -20/-2

x^2 =10

take the square root on each side

sqrt(x^2 )=±sqrt(10)

x = ±sqrt(10)

check:

5 - 2x² = -15

+sqrt(10)

5 - 2(sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15

-sqrt(10)

5 - 2(-sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15