<span>Divide by 3 get a remainder of 2
5, 8, 11, 14, 17, 20, ...
Divide by 5 get a remainder of 2
7 , 12, 17, 23, ...
Divide by 7 get a reminder of 5
12, 19, 26, 33, ...
And find a number in all three lists
</span>
<span>Not the most convenient way for sure, but since 47 works it will not take too long</span><span>
</span>
Answer:
x = 9
Step-by-step explanation:
For the lines to be parallel, then
9x + 8 and 15x - 46 are alternate angles and congruent, thus
15x - 46 = 9x + 8 ( subtract 9x from both sides )
6x - 46 = 8 ( add 46 to both sides )
6x = 54 ( divide both sides by 6 )
x = 9

so we have those critical values, which gives us the intervals of (-∞, 0] , [0, 6] and [6, +∞).
where is it increasing or decreasing? well, that's just a matter of checking a value on each region for the the first derivative, namely the first derivative test.
we can check for f(-1) = 12(-1)² - 72(-1), is a positive value, increasing.
and check f(1) = 12(1)² - 72(1), is a negative value, decreasing.
and check f(7) = 12(7)² - 72(7), positive, so increasing.
check the picture below, and you can see there which are the minima or maxima.