Chứng minh mệnh đề sau bằng phương pháp phản chứng: " Nếu phương trình bậc hai ax2+bx+c=0 vô nghiệm thì a và c cùng dấu"

Colin listed his assets and liabilities on a personal balance sheet. colin’s balance sheet (august 2013) assets liabilities cash $1,500 credit card $500 stocks $800 rent $800 car $5,000 car loan $1,200 coin collection $1,200 student loan $5,000 total total which statement is true about the total assets and the total liabilities? the total of the assets and the liabilities are the same. the total of the assets is greater than the total of the liabilities. the total of the assets is less than the total of the liabilities. the total of the assets cannot be compared to the total of the liabilities.

Haruka hiked several kilometers in the morning. she hiked only 66 kilometers in the afternoon, which was 25% less than she had hiked in the morning. how many kilometers did haruka hike in all?

Can someone me out here number 4 plz