One day, a teacher entered the classroom and told the students they would have a surprise test. After hearing that, all students were seated excitedly and waited for the test to begin soon. Then, the teacher gave the test papers to all students. However, the students were confused(困惑的)to see that there were no questions but just a black dot(点)in the center of the page. The teacher noticed the students' facial expressions and told them, "I want you to write about what you see there."

    The students were still confused but got started with the test. At the end of the class, the teacher took all the answer sheets and started reading each answer in front of all students. All of them described about the black dot and tried to explain its position. After the teacher finished reading, the whole class was silent.

    Then, the teacher began to explain. "Don't worry. I am not going to give you grades for this, but I just want you to think about something. Here everyone focused(聚焦)on the black dot and wrote about it, but no one wrote about the white paper, the same is with our lives. The white paper represents(象征)our whole life and the black spot represents problems in our life."

    Our life is a gift given to us by God, with love and care, and we always have reasons to celebrate-our friends around us , the job that provides us with livelihood , the miracles(奇迹)we see every day. Still we just focus on day to day problems like health issues, lack of money, problems in relationships and so on, but we never see that these problems are very small, compared to everything we have in our lives. So we should try to be happy and live life positively.

已知极点为直角坐标系的原点，极轴为x轴正半轴且单位长度相同的极坐标系中曲线C₁：ρ=1， $C_2：\{\begin{array}{c}x=\frac{\sqrt{2}}{2}t-1\\ y=\frac{\sqrt{2}}{2}t+1\end{array}$ （t为参数）．

两直线l₁与l₂平行可表示为____．