So we know that surface area is top circle +bottom circle+ (circumfurence times height so) 2(π(radius)^2)+(height(2π(r))) so fill in the blanks it's kind of hard to see but πr means pi times radius (r) 2πr^2+((4.2)(2)(π)(r))=628.3 factor out the 2 so the equation would mean 2((πr^2)+(4.2πr))=628.3 divide both sides by 2 πr^2+4.2πr=314.15 what's interesting is that the first few digits of pi are 3.1415 so we aproximate pi as 3.14 and divide both sides by 3.1415 r^2+4.2r=100 subtract 100 from both sides r^2+4.2r-100=0 factor (x-8.11812)(x+12.3181)=0 so (if xy=0 then x or/and y must be 0 so)we set them to 0 so x-8.11812=0 x=8.11812
second one x+12.3181=0 x=-12.3181 since radii (or any legnth) cannot be negative, we can cross this solution out so
