10 xy + 3y + 20 ax + 6a = y(10x+3) + a(20x+6) = y(10x+3)+2a(10x+6)=
(y+2a)(10x+3)
5³ is 5x5x5 so that is 125
To construct a perpendicular bisector you set the compass to a span which is greater than half the length of the given line. Then setting the point at one end of the line construct an arc passing through the line . Then repeat this process from the other side of the line keeping the compass at the same setting.
Now draw the perpendicular bisector through the 2 intersections of the arcs. That's it.
You would do 3/4 of 20.
20 / 4 = 15
15 pens have black ink.
