x2 – 10x + 21 write in notebook
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x² - 10x +21
= x² +( 7 +3 )x + 21
= x² + 7x +3x + 21
= x(x + 7) + 3(x+ 7)
= (x+ 3)(x + 7)
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Answer:
(x+3)(x+7)
Step-by-step explanation:
firstly the largest power is x^2 so when factorising we know that both brackets must involve an x plus or minus a number.
next we look at the 21 and we need two numbers that multiply together to get this number, the two sets of numbers that multiply to get this is 1 and 21 and 3 and 7.
then we take these two sets of numbers and we look at the 10x this means the numbers must add/subtract to give ten, this means the answer must use the 3 and 7 as they add to give 10
therefore our answer is (x+3)(x+7)
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