Answer:
1) Perimeter is when you add all the side lengths up, so make an equation:
(x+2) + 2x + (2-x) = 18
Getting rid of parentheses:
x+2+2x+2-x = 18
Combine like terms:
2x+4=18
Getting term with x alone by subtracting 2 from both sides:
2x=14
Get x alone by dividing both sides by 2:
x=7
Check it:
(7+2) + 2(7) + (2-7) = 18
9 + 14 -5 = 18
23 - 5 = 18
18 = 18
2a) Equation for area of a circle is A=πr²
Diameter is 2 times the radius, so if diameter is 4cm, radius is 2cm
A=π•2²
= 4π ~~~ I am using the pi button on the calculator
≈ 12.57 cm² (rounded to hundredth) ----- (this would be 12.56 if you're using 3.14 instead of the pi button)
2b) Equation for circumference of a circle is C=2πr
C=2•π•2
= 4π
≈ 12.57 cm (if you notice, this answer would be the same as 2a.)
3a) Go backwards and do the opposite of what it tells you. Start with 28 and add 25 to get 53. I'm assuming the question means 'triple it' instead of 'treble it', so you would actually divide by 3 instead of multiplying. 53÷3 = 17 2/3. (I've made sure I've done this right by following the steps forward and it should be correct)
3b) Again, go backwards and do the opposite. Starting with 9, add 21 to get 30. Instead of multiplying by 2, divide by 2 to get 15. (I've also checked this one too)
4a) 5x-7=9-3x ---Start by getting the same terms on either side of the equal sign. I will be putting the terms with x on the left by adding 3x to both sides
8x-7=9 ---Now, I will put the constant term on the right side by adding 7 to both sides.
8x=16 ---Divide both sides by 8 to get x alone:
x=2
Check:
5(2)-7 = 9-3(2)
10-7 = 9-6
3 = 3
4b)
-11=7 ---Get the x term alone by adding 11 to both sides
=18 ---Multiply both sides by 3 to get x alone
x=54
Check:
-11 = 7
18-11 = 7
7 = 7
5) y=12-2x
Fill in each value for x.
x = -2:
y=12-2(-2)
y=12-(-4) ---Subtracting a negative makes both signs positive
y=12+4
y=16
x = 0
y=12-2(0) ---Anything multiplied by zero becomes zero
y=12
x = 3
y=12-2(3)
y=12-6
y=6