Many years in school could not memorize the multiplication tables, so getting out of the situation instantly folding in mind...I'm still not firmly remember...was full DiBella that gave me a great opportunity brilliantly to take the examination on the Mat.Sciences in the best University of the evil Empire...So me solve this example is extremely simple in mind and was in 9 years, and now even more so...
Will complicate the task itself, identifying 10 for X!!!...We are automatically in the mind will solve the problem more complicated: 50x50+h+h+h+h+h Here X=50...And you can take, for example X=1000000001...and I have in mind will give You, without batting an eye, the answer earlier than You would rape his wretched calculator...
Have(I do this in the mind), but explain to others, who know the multiplication table...
X squared + (X+1)squared+etc....Knowing the well-known formula , which is easy to derive in the mind (X+Y)x(X+Y)=Xxx+HHO+Ear...in the numerator of the y is equal to 1, then 2, 3 and 4...Disclose the sums of squares...
Have numerators 5 X squared plus double works X take out the brackets: 5xxx+ 2(1+2+3+4) + 1x1+2x2+3x3+4x4=5xxx+20xx+30...replacing X, 10: HH+20x10+30=730...If X=50, we have h+20x50+30=12500+1030=13530...