How do you solve #21n ^ { 2} + 5n - 6= 0#?
2 Answers
Explanation:
Given:
Now, If :
And If :
Hence Explained.
Explanation:
#"factorise the quadratic using the a-c method"#
#"that is factors of "21xx-6=-126" which sum to "+5#
#"the factors of "-126" which sum to + 5 are + 14 and - 9"#
#color(blue)"split the middle term using these factors"#
#rArr21n^2+14n-9n-6=0larrcolor(blue)"factor by grouping"#
#rArrcolor(red)(7n)(3n+2)color(red)(-3)(3n+2)=0#
#"take out the common factor "(3n+2)#
#rArr(3n+2)(color(red)(7n-3))=0#
#"equate each factor to zero and solve for n"#
#3n+2=0rArrn=-2/3#
#7n-3=0rArrn=3/7#