And?... is that the question or is there more?
Answer:
70
Step-by-step explanation:
- for the value of difference to be largest, the minuend should be maximum(most possibly) and the subtrahend should be minimum
[in A-B=X, A is minuend and B is subtrahend ]
- so, $a.b should be maximum. as there is a condition that 4 digits should be distinct, the product will be maximum if we choose 2 maximum valued numbers from the given numbers. so, one of them should be 9 and the other should be 8.
therefore, $a.b=9*8=72
- as mentioned above, c.d$ should be minimum. this will be possible only when we choose 2 minimum valued numbers from the given numbers. so, one of them should be 1 and the other should be 2.
therefore, c.d$ = 1*2 = 2
- hence, the difference = 72-2 = 70
- thus, the largest possible value of the difference $a.b - c.d$ = 70
Recall the binomial theorem.

1. The binomial expansion of
is

Observe that


When we multiply these by
,
•
and
combine to make 
•
and
combine to make 
and the sum of these terms is

2. The binomial expansion is

We get the
term when
:

Step-by-step explanation:
first you have to do the subtraction in the parentheses so it's 8+3(4) and then you multiply the 3 by 4 (only the 3 because the 8 isn't next to the multiply) and then you have 12, add 8 and it's 20
58=7/4x
Multiply both sides by 4 so the fraction cancels out:
232=7x
Divide both sides by 7:
x=33.14 (rounded)
Hope this helps :)