The authors study approximations \({\mathcal L}_ A f\), \({\mathcal L}_ B f\) and \({\mathcal L}_ C f\) to a function \(\{f(x)\), \(x_ 0\leq x\leq x_ N\}\) from the space that is spanned by the multiquadrics \(\{\varphi_ j\): \(j=0,1,\dots,N\}\), and by linear polynomials, where \(\varphi_ j(x)=[(x- x_ j)^ 2+c^ 2]^{1/2}\), \(x\in R\) and \(c\) is a positive constant. They define these approximations by quasi-interpolation formulas that are shown to give a good accuracy even if the distribution of the centres in \([x_ 0,x_ N]\) is very irregular.