a: \(A=15-16+17-18+19-20+21-22+23-24\)=(15-16)+(17-18)+(19-20)+(21-22)+(23-24)=(-1)+(-1)+(-1)+(-1)+(-1)=-5b: B=10-11+12-13+...+98-99+100=(10-11)+(12-13)+...+(98-99)+100=(-1)+(-1)+...+(-1)+100Từ 10 đến 99 có (99-10):1+1=99-10+1=90(số)=>\(B=\left(-1\right)\cdot\dfrac{90}{2}+100=-45+100=55\)c: \(C=10+11-12-13+14+15-16-17+18+19-20-21\)=(10-12)+(11-13)+(14-16)+(15-17)+(18-20)+(19-21)=(-2)+(-2)+...+(-2)=-12d: \(D=1-2-3+4+5-6-7+8+9-10-11+12+13-14-15+16\)=(1-2-3+4)+(5-6-7+8)+(9-10-11+12)+(13-14-15+16)=0+0+0+0=0f: \(E=20-21-22+23+24-25-26+27+...+60-61-62+63\)\(=\left(20-21-22+23\right)+\left(24-25-26+27\right)+...+\left(60-61-62+63\right)\)\(=0+0+...+0\)=0g: Sửa đề: \(G=1+3-5-7+9+11-13-15+...-397-399\)\(=\left(1+3-5-7\right)+\left(9+11-13-15\right)+...+\left(393+395-397-399\right)\)\(=\left(-8\right)+\left(-8\right)+...+\left(-8\right)\)Dãy số này có \(\dfrac{399-1}{2}+1=\dfrac{398}{2}+1=199+1=200\left(số\right)\)=>\(G=\left(-8\right)\cdot\dfrac{200}{4}=-8\cdot50=-400\)Câu trả lời: a: \(A=15-16+17-18+19-20+21-22+23-24\)=(15-16)+(17-18)+(19-20)+(21-22)+(23-24)=(-1)+(-1)+(-1)+(-1)+(-1)=-5b: B=10-11+12-13+...+98-99+100=(10-11)+(12-13)+...+(98-99)+100=(-1)+(-1)+...+(-1)+100Từ 10 đến 99 có (99-10):1+1=99-10+1=90(số)=>\(B=\left(-1\right)\cdot\dfrac{90}{2}+100=-45+100=55\)c: \(C=10+11-12-13+14+15-16-17+18+19-20-21\)=(10-12)+(11-13)+(14-16)+(15-17)+(18-20)+(19-21)=(-2)+(-2)+...+(-2)=-12d: \(D=1-2-3+4+5-6-7+8+9-10-11+12+13-14-15+16\)=(1-2-3+4)+(5-6-7+8)+(9-10-11+12)+(13-14-15+16)=0+0+0+0=0f: \(E=20-21-22+23+24-25-26+27+...+60-61-62+63\)\(=\left(20-21-22+23\right)+\left(24-25-26+27\right)+...+\left(60-61-62+63\right)\)\(=0+0+...+0\)=0g: Sửa đề: \(G=1+3-5-7+9+11-13-15+...-397-399\)\(=\left(1+3-5-7\right)+\left(9+11-13-15\right)+...+\left(393+395-397-399\right)\)\(=\left(-8\right)+\left(-8\right)+...+\left(-8\right)\)Dãy số này có \(\dfrac{399-1}{2}+1=\dfrac{398}{2}+1=199+1=200\left(số\right)\)=>\(G=\left(-8\right)\cdot\dfrac{200}{4}=-8\cdot50=-400\)