18. s = 5r^2 + 7......making r the subject
s - 7 = 5r^2
(s - 7) / 5 = r^2...by taking the sqrt of both sides, it eliminates the ^2
( sqrt (s-7)/5) = r
19. h = ut - 1/2gt^2....u = 100, t = 1 4/5(or 9/5)...g = 6.4
h = (100)(9/5) - 1/2(6.4)(9/5^2)
h = 180 - 1/2(6.4)(3.24)
h = 180 - 3.2(3.24)
h = 180 - 10.368
h = 169.632 or 169 79/125
20. sorry..do not know this one
7.8 times 10^5
Step 1
To find a, take the number and move a decimal place to the right one position.
Original Number: 780,000
New Number: 7.80000
Step 2
Now, to find b, count how many places to the right of the decimal.
New Number: 7 . 8 0 0 0 0
Decimal Count: 1 2 3 4 5
There are 5 places to the right of the decimal place.
Step 3
Building upon what we know above, we can now reconstruct the number into scientific notation.
Remember, the notation is: a x 10b
a = 7.8 (Please notice any zeroes on the end have been removed)
b = 5
Now the whole thing:
7.8 x 10^5
Step 4
Check your work:
10^5 = 100,000 x 7.8 = 780,000