The area of a rectangle can be expressed by 2x2 – 7x – 4. If the rectangle has an area of 45, find the positive value for x.

7

Step-by-step explanation:

2x^2 - 7x - 4 = 45

2x^2 - 7x - 49 = 0 : subtract 45 from both sides

Quadratic formula:

  x = (7 ± sqrt(7^2 - 4*2*-49) ) / 4

  x = (7 ± sqrt(49 - -392)) / 4

  x = (7 ± sqrt(441)) / 4

  x = (7 ± 21) / 4

  x = (7 + 21) / 4 OR x = (7 - 21) / 4

  x = 28 / 4 OR x = -14 / 4

  x = 7 as it is the only positive answer

a 4/6 = 9/12   not proportional

step-by-step explanation:

to find which are not proportional, we can use cross products

if it is true, they are proportional.   if it is not true, they are not proportional.

a 4/6 = 9/12

4* 12 = 6*9

48 = 54

not this is not proportional  

b 2/3 = 12/18  

2* 18 = 3 * 12

36 = 36

this is proportional

c 5/4 = 10/8  

5*8 = 4*10

40 = 40

this is proportional

d 7/5 = 35/25

7*25 = 5 * 35

175 = 175

is proportional