392)
the number 8b is divisible by 4
so b can be 0,4,8
a+b+30 is divisible by 9
putting b=0 , we get a=6 to get nearest multiple of 9.. but 2456784 is ot divisible by 72
putting b=4 we get a=2
2456784 is divisible by 72
so a=2, b=4
Well, here are some brainy problems you might want to have a look at only if you are not feeling too sleepy --- :)
I am gonna post the solutions after one hour if I can ---
1> If y = xx2+1 , then find x if d4dx4(y) = -3.
2> " a45678b " is such a number that is divisible by 72. Find " a " and " b " if they are digits.
3> If a+b+c = 0;
then the eqn. nax2 + mbx + lc =0 has at least one root in the interval --- ???
-
UP 0 DOWN 0 0 6
6 Answers
39
1@b555 your method is okay but you have to take cases and compute so many things --- think i have better solution ---
as the number is divisible by 72 and (8,9)=1 so the number is divisible by 8 as well as 9.
so a+b+30 = 0(mod 9) ----- (1)
and a number is divisible by 8 if the sum of its last 3 digits is a multiple of 8 .
so 700 + 80 + b = 0(mod 8)
or 780 + b =(mod 8)
which gives b = 4 only. --- (2)
so a should be 2 from (1) and (2).
1Yup i have already got no. 1 .please tell what substitution should be taken.
39i do not agree with u...
there is nothing called cases and so many things in what i have done...
its just 2 points...
and simple addition
1IN D FIRST 1,u can write y= (1/2)*( 2x/x^2 +1 ) n put x= tanx n
y is den (1/2)*sin 2x...................................am i right???
coz tanx can assume any value