`a)`
`(3x+1)(x-2)=3x^2-6x+x-2=3x^2-5x-2`
`b)`
`(7-x)(2x+4)=14x+28-2x^2-4x=-2x^2+10x+28`
`c)`
`2x(x-5)+x^2-4x=2x^2-10x+x^2-4x=3x^2-14x`
`d)`
`-3x(2x+1)+x(x-2)=-6x^2-3x+x^2-2x=-5x^2-5x`
`e)`
`x^2-8x(x-1)(3x-2)=x^2-8x(3x^2-5x+2)`
`=x^2-24x^3+40x^2-16x`
`=-24x^3+41x^2-16x`
`f)`
`(7x-1)(x+2)-3x(x-4)=7x^2+13x-2-3x^2+12x`
`=4x^2+25x-2`
Đáp án:
Giải thích các bước giải:
a,(3x+1)(x-2)=3x² -6x+x-2 =3x²-5x-2
b, (7-x)(2x+4)=14x+28-2x²-4x= -2x²+10x+28
c, 2x(x-5)+x²-4x =2x²-10x +x²-4x= 3x²-14x
d, -3x(2x+1) +x(x-2) =-6x²-3x +x²-2x =-5x²-5x
e, x²-8x(x-1)(3x-2) =x²-8x(3x²-5x+2) =x²-24x³ +40x²-16x = -24x³ +41x²-16x
Ex2: Choose the best option 6. Someone discovered penicillin in 1928, _________? A. hadn’t he/she B. didn’t he/she C. didn’t someone D. wasn’t he/she 7. You stayed home last night, _________? A. had you B. would you C. didn’t you D. did you 8. The poor don’t have many things to eat, _________? A. do we B. do they C. do you D. do I 9. The teacher asked you if you finished your homework that day, __________? A. hadn’t he B. didn’t he C. didn’t you D. hadn’t he 10. You were driving home when you saw Lan, _________? A. didn’t you B. weren’t you C. wouldn’t you D. hadn’t you 11. You are thirsty, __________? A. don’t you B. aren’t you C. are you D. are not you 12. Nam wishes he had worked hard last year, __________? A. hadn’t Nam B. hadn’t he C. doesn’t Nam D. doesn’t he 13. Not only the women but also the men _________ watching this programme. A. like B. has liked C. is liking D. likes 14. Neither the students nor the teacher ___________ raincoats. A. taking B. takes C. are taking D. take 15. You had had breakfast before you went to school yesterday, ___________? A. hadn’t you B. didn’t you C. wouldn’t you D. weren’t you 16. _________ ten minutes earlier, we would have got better seats. A. If we had not arrived B. Had we arrived C. Did we arrive D. If we arrived 17. Only when you grow up, __________ the truth. A. did you know B. will you know C. you would know D. you will know 18. You could ride a bicycle when you were five, ___________? A. hadn’t you B. didn’t you C. weren’t you D. couldn’t you 19. There have been many achievements since the country carried out economic reforms, ________? A. don’t there B. haven’t they C. haven’t there D. don’t they 20. People who exercise frequently are healthier than those who ____________. A. exercise B. do C. don’t D. are
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g. situx(1 + cos2x} + sin2x = 1 + cOSA, i. (2+ain²x)cosx + (1+cos³x)sinx = 1+ sin2x.
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