Let $L^2([0,1],x)$ be the space of the real valued, measurable,square summable functions on $[0,1]$ with weight $x$, and let ${\calL}_n$ be the subspace of $L^2([0,1],x)$ defined by a linearcombination of $J_0(\mu_kx)$, where $ J_0 $ is the Bessel functionof order $0$ and $\{\mu_k\}$ is the strictly increasing sequence ofall positive zeros of $J_0$. For $f\in L^2([0,1],x),$ let $E(f,{\cal L}_n)$ be the error of the best $L^2([0,1],x)$, i.e.,approximation of $f$ by elements of ${\cal L}_n.$ The shift operatorof $f$ at point $x\in [0, 1]$ with step $t\in [0, 1]$ is defined by$$T(t)f(x)=\frac{1}{\pi}\int_0^{\pi}f\big(\sqrt{x^2+t^2-2xt\cos\tz}\big)d\tz.$$The differences $(I-T(t))^{r/2}f=\sum_{j=0}^{\infty}(-1)^j{{r/2}\choose{j}}T^j(t)f$ of order $r\in (0, \infty)$ and the$L^2([0,1],x)-$ modulus of continuity$\omega_r(f,\tau)=\sup\{\|(I-T(t))^{r/2}f\|: 0 \leq t\leq \tau \}$of order $r$ are defined in the standard way, where $T^0(t)=I$ isthe identity operator. In this paper, we establish the sharp Jacksoninequality between $E(f, {\cal L}_n)$ and $\omega_r(f,\tau)$ forsome cases of $r$ and $\tau$. More precisely, we will find thesmallest constant $\ck_n(\tau, r)$ which depends only on $n, r, $and $\tau,$ such that the inequality $E(f, {\cal L}_n)\le\ck_n(\tau, r)\omega_r(f,\tau)$ is valid.