Step-by-step explanation:
you must have learned about Pythagoras in right-angled triangles :
c² = a² + b²
where c is the Hypotenuse (the baseline opposite of the 90° angle), and a and b are the other 2 sides (called the legs).
right-angled triangles just means that one angle in the triangle is 90° (called a right angle).
the little square symbol in the top angle tells us that here we have a right angle.
so, we can use the Pythagoras rule :
bottom² = 7² + 10² = 49 + 100 = 149
bottom = sqrt(149) = 12.20655562...
oh, and "sqrt" is short for square root.
and you do understand squaring a number and taking the square root of a number ?
a² = a × a (multiplying a number by itself)
sqrt(a) = b, so that b × b = b² = a
