If
21 = 42
39 = 618
17 = 214
then what does
45 = ?

810

Step-by-step explanation:

21 = 42

Decode:

Number in the tens place = 2 x 2 = 4

Number in the ones place = 1 x 2 = 2

42

39 = 618

Decode:

Number in the tens place = 3 x 2 = 6

Number in the ones place = 9 x 2 = 18

618

17 = 214

Decode:

Number in the tens place = 1 x 2 = 2

Number in the ones place = 7 x 2 = 14

214

Find 45

Number in the tens place = 4 x 2 = 8

Number in the ones place = 5 x 2 = 10

810

{x = -1/2 ,   y = -1

step-by-step explanation:

solve the following system:

{2 x + y = -2

{10 x - 3 y = -2

in the first equation, look to solve for y:

{2 x + y = -2

{10 x - 3 y = -2

subtract 2 x from both sides:

{y = -2 x - 2

{10 x - 3 y = -2

substitute y = -2 x - 2 into the second equation:

{y = -2 x - 2

{10 x - 3 (-2 x - 2) = -2

10 x - 3 (-2 x - 2) = (6 x + 6) + 10 x = 16 x + 6:

{y = -2 x - 2

{16 x + 6 = -2

in the second equation, look to solve for x:

{y = -2 x - 2

{16 x + 6 = -2

subtract 6 from both sides:

{y = -2 x - 2

{16 x = -8

divide both sides by 16:

{y = -2 x - 2

{x = -1/2

substitute x = -1/2 into the first equation:

{y = -1

{x = -1/2

collect results in alphabetical order:

answer:   {x = -1/2 ,   y = -1