Is 21 km, 28 km, 35 km, a right triangle

What is the smallest integer n such that n\sqrt{2} is greater than 20

Find the magnitude, correct to two decimal places, made by each of the following with positive direction of the x axis a) y= x the answer is 45° but i don’t know how

In a two-digit number the units' digit is 7 more than the tens' digit. the number with digits reversed is three times as large as the sum of the original number and the two digits. find the number.