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Confusion with binomial question...? (C4)

The question is:

first, expand (1-4x)^1/4 to x^3
I already expanded, it is 1-x-3/2x^2-7/2x^3

but the confusion starts there

"The term of the lowest degree in the expansion of
(1+ax)(1+bx^2)^7-(1-4x)^1/4
in ascending powers of x is the term in x^3.
Find the values of the constants a and b.

The link below, I'm not showed how he got to that answer.




https://www.youtube.com/watch?v=dMjodsY8vNw&index=4&list=PLtIRdxuyNbI9UHZjznfe8HSmAmhy5YubM
The term of lowest degree is the term in x^3. Thus the coefficients of the constant term, term in x, and term in x^2 must also be 0. After multiplying out (1+ax)(1+bx^2)^7 and subtracting what you got in the first part, you can then use this information to form equations in a and b. This should then allow you to find their values.
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TeeEm
19
Original post by hunihuni
The question is:

first, expand (1-4x)^1/4 to x^3
I already expanded, it is 1-x-3/2x^2-7/2x^3

but the confusion starts there

"The term of the lowest degree in the expansion of
(1+ax)(1+bx^2)^7-(1-4x)^1/4
in ascending powers of x is the term in x^3.
Find the values of the constants a and b.

The link below, I'm not showed how he got to that answer.




https://www.youtube.com/watch?v=dMjodsY8vNw&index=4&list=PLtIRdxuyNbI9UHZjznfe8HSmAmhy5YubM


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