Because it was reflected across the x axis, the distance between the two points is twice the distance of the old point from the x axis, and the distance from the old point from the x axis equals the distance from the new point to the x axis. The distance from the x axis is the absolute value of the x=y value. 7.5 is the y value, meaning the point is 7.5 units away from y=0, the x axis. The new point is twice this from the old point. 7.5 x 2 = 15. The new point is 15 units away from the old point.
Ni : Zn: Cu = 7:2:9 =7x : 2x : 9x
7x+2x+9x = 3.8
18x=3.8
x=3.8/18=1.9/9≈0.21
Ni: 7x=7*0.21=1.47 ≈1.5 kg
Zn: 2x=2*0.21=0.42≈0.4 kg
Cu: 9x=9*0.21=1.89 ≈1.9 kg
Check 1.5+0.4+1.9 =3.8 True
Here is the set up:
Let m = mass of the block
m = (30•40•50)/(2.8)
Use your calculator to calculate the left side for m.
1) The expressions are not equivalent. When you expand and multiply 2(x + 3) it becomes 2x + 6. This is not equal to 3x + 5
2) They are equivalent. Again, expand and multiply the second expression. 2(3n + 4) becomes 6n + 8. This makes both sides equal.
3) They are equivalent. In the parentheses, you are adding 3 y's and a 2. This gives you 3y + 2. Now add the additional 3y that follows the closed parentheses. You'll have 6y + 2. Now both sides are equivalent.