如果已知F,i,n,求P,则P=F×（P／F,i,n)。（)

A.题目形式为已知5年后8万元为终值，求现在存入多少钱为现值，所以为已知终值求现值

B.查表法需要用到1元现值的终值系数(F/P,i,n)

C.查表法需要用到1元终值的现值系数(P/F,i,n)

D.Excel函数法，需要调用现值函数PV(6%，10，-80000，0,0)

A.F=A(P/A，I，n)(F/P，i，n)

B.F=A(A/F，i，n)

C.F=A(P/A，i，n)(P/F，i，n)

D.F=A(F/A，i，n)

E.F=A(A/P，i，n)(P/F，i，n)

A.(F/P, i, n) = (F/P, i, n1) + (F/P, i, n2)

B.(F/P, i, n) = (F/P, i, n1)×(F/P, i, n2)

C.(P/F, i, n) = (P/F, i, n1) + (P/F, i, n2)

D.(P/F, i, n) = (P/F, i, n1)×(P/F, i, n2)

A.(F/P, i, n) = (F/P, i, n1) + (F/P, i, n2)

B.(F/P, i, n) = (F/P, i, n1)×(F/P, i, n2)

C.(P/F, i, n) = (P/F, i, n1) + (P/F, i, n2)

D.(P/F, i, n) = (P/F, i, n1)×(P/F, i, n2)

A.(F/P, i, n) = (F/P, i, n1) + (F/P, i, n2)

B.(F/P, i, n) = (F/P, i, n1)×(F/P, i, n2)

C.(P/F, i, n) = (P/F, i, n1) + (P/F, i, n2)

D.(P/F, i, n) = (P/F, i, n1)×(P/F, i, n2)

A.A(F/A，i，n)(P/F，i，n)

B.A(P/A，i，n+1)

C.A(F/A，i，n+1)(P/F，i，n)

D.A(P/A，i，n+1)(F/P，i，1)

E.A+A(P/A，i，n)

如图所示平面桁架由长度l=1m，直径d=40mm的圆截面杆构成，已知E=206GPa，λ_p=100，λ_s=60，中长杆材料系数a=460MPa，b=2.567MPa，安全因数[n]=3，(1)试求许可载荷F；(2)如果载荷方向相反(向里)，许可载荷F是否改变？若改变则其值为多少？